Characterisation of landfills for recovery of methane and control of emissions

Abstract

Different types of municipal solid waste (MSW) landfills were characterized according to waste and leachate sampling, on-line measurements of internal leachate and landfill gas monitoring to provide information for both active landfill and postlandfill operations in boreal conditions. The study showed that waste and internal leachate, organic and nitrogen content, and biological methane potential (BMP) as well as their distribution can to a certain extent be characterised in landfills with unknown/undetermined contents. All parameters showed high horizontal and vertical variation in each landfill indicating that both the composition and state of degradation of waste varied greatly in these landfills. For example, the BMP (range 1-183 m3/t total solids (TS) and 6-60 m3/t TS in the 20- and 50-years-old landfills, respectively), volatile solids (VS, range 35-89 % and 3-80 %) and leaching of ammoniumnitrogen (range 0-2205 g/t TS and 0-1400 g/t TS) were higher in the 20-year-old than 50-year-old landfill. The rates of methane generation and potential between the landfills were different, as indicated by the first order kinetic methane generation rate (k) and methane generation potential (L)۪ for bulk waste, which, on the basis of experimentally determined methane potentials and modelling in addition to actual landfill methane recovery, were 0.17 and 130 m3/t in the 20-year-old and 0.05 and 40 m3/t in the 50-year-old landfills, respectively. The mechanically and mechanicallybiologically treated MSW residuals were characterized by different nitrogen and organic matter budgets as well as different leachate and gas properties. The mechanically treated MSW residuals prolonged by at least two years the acidogenic phase of degradation (pH 5.8-6.1) and leaching of ammonium nitrogen (391 g/t TS; 8 % of initial nitrogen content) and organic matter (24 kg COD /t TS), while with biologically treated residuals the methanogenic phase of degradation was reached (pH >7) after a few months and the leaching of ammonium nitrogen (79 g/t TS; 1 % of initial content) and organic matter (0.6 kg/t TS) were significantly lower during the 14-month study period.